Method of making an electrode having a filament with extending legs

ABSTRACT

An electrode, such as for a fluorescent lamp, is made by providing a helically wound filament, attaching the filament near the ends thereof to a pair of support wires, temporarily holding an intermediate portion of the filament, and pulling or stretching turns of the filament between the held intermediate portion and the lead wires to form legs on the filament.

United States Patent I [191 Lemmers METHOD OF MAKING AN ELECTRODE HAVINGA FILAMENT WITH EXTENDING LEGS M [75] Inventor: Eugene Lemmers,Cleveland Heights, 01116 [73] Assignee: General Electric Company,

Schenectady, NY.

22 Filed: Mar. 28, 1973 211 A 1.1\16.;34s,s64-

52 us. c1. l40/7l.6, 29/2515 51 1111.01 B21f 45/00 [58] Field of Search140/7l.6; 29/2513, 25.15

[56] References Cited UNITED STATES PATENTS 3,058,497 10/1962 Buckl40/7l.6

[ 1 June 18, 1974 3,073,356 1/1963 Rowan et '61 140/71.6 3,096,7957/1963 LCHZ l40/71.6 3,160,181 12/1964 Voyce et a1... l40/71.6 3,629,91412/1971 Giertsen 140/716 Primary Examiner-Lowell A. Larson Art0r ney,Agent, or Firm-Norman C. Fulmer; Lawrence R. Kempton; Frank L. Neuhauser571 ABSTRACT An electrode, such as for a fluorescent lamp, is made byproviding a helically wound filament, attaching the filament near theends thereof to a pair of support wires, temporarily holding anintermediate portion of the filament, and pulling or stretching turns ofthe filament between the held intermediate portion and the lead wires toform legs on the filament.

4.Claims, 5 Drawing Figures 1 METHOD OF MAKING AN ELECTRODE HAVING AFILAMENT WITH EXTENDING LEGS BACKGROUND OF THE INVENTION The inventionis in the field of making filament-type electrodes for use in electricdischarge lamps such as fluorescent lamps.

Fluorescent lamps generally comprise a pair of electrodes respectivelysealed into the ends of an elongated glass envelope which contains acombination of gases at suitable pressure for causing an electricdischarge when voltage is applied across the electrodes. Each of thelamp electrodes comprises one or more elongated filaments carried by alead-in wire arrangement. The filaments are coated with suitableelectron emission materials so as to function as cathodes, i.e., asource of electrons for current flow in the lamp. The lamp electrodesmay also be provided with anode elements, or in some cases, the cathodesmay also function as anodes to receive the discharge electron flow onalternate halfcycles of a-c electrical energy.

In a typical electrode construction, the filament is held -by a pair oflead-in support wires bent so as to clamp against the elongatedhelically'coiled filament near the two ends thereof, respectively. Thelead-in wires support the filament and function to carry current to theelectric discharge in the lamp, and also function to carry heatingcurrent to the filament in preheat and rapid start types of lamps. Aftera filament is attached to the support wires, an electron emissionmaterial is coated onto an intermediate portion of the filament betweenthe support wires, and is heated by passing current through the filamentto volatilize and drive off a binder that was in the emission material.It is important that the emission mix not be applied to the supportwires nor to the filament near the support wires, as these regions willnot get hot enough to volatilize the binder, and binder remaining atthese regions in a lamp will give off gases that will degrade lampperformance.

One technique for making the helically coiled elongated filaments so asto facilitate applying emission mix to the desired intermediate portionis to provide each filament with a pair of legs consisting of endportions of the filament wire extending axially outwardly from theotherwise closely coiled filament. The support wires are bent around, soas to be clamped against, the two legs. When the emission mix is appliedto the coiled intermediate portion of the filament, the parts of thelegs between the support wires and the coiled portion of the filamentprevent the emission material from creeping toward the support wireclamps. A disadvantage of this technique is that, in automaticproduction equipment for feeding the filaments to the support wires, thefilaments tend to get tangled and jammed due to legs of some filamentsengaging with the helical wound portions to other filaments. Anothertechnique, disclosed in U.S. Pat. Nos. 2,479,192 and 2,479,l93, insteadof providing legs on the filament, is to provide a widely spaced turnnear each end region of the filament. When the end regions of thefilament have been in automatic machinery for the filaments to gettangled and jammed together at their widely spaced turns.

SUMMARY OF THE INVENTION In a preferred method of the invention, anelectrode, such as for a fluorescent lamp, is made by the steps ofproviding a helically wound filament (not provided with legs at the endsthereof), attaching the filament near the ends thereof to a pair ofsupport wires, temporarily holding an intermediate portion of thefilament, and pulling or stretching turns of the filament between theheld intermediate portion and the lead wires so as to form legs on thefilament. The legs can be formed by slightly spreading apart the supportwires. Thus, the closely wound helical filaments are readily handled byautomatic production machinery without becoming tangled together, andalso the filaments are provided with legs at the ends thereof prior toapplying the emission material, thereby preventing the emission materialfrom creeping toward the support wires.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cutaway side view of theend portion of a fluorescent lamp, showing an electrode made inaccordance with the invention;

FIG. 2 is a side view of an electrode structure in which a helicallycoiled filament has been clamped near the ends thereof by a pair ofsupport wires;

FIG. 3 illustrates the step of holding an intermediate portion of thefilament prior to pulling legs on it;

FIG. 4 illustrates the step of pulling legs on the filament by spreadingapart the support wires while the interrnediate region of the filamentis being held; and

FIG. 5 is a side view of the completed electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The lamp shown in FIG. 1comprises an elongated tubular glass bulb 11 having a coating ofphosphor mate rial 12 on the inner surface thereof. An electrode 13 issealed at each end of the bulb, respectively, in wellknown manner. Theelectrode 13 comprises a filament or cathode 16 attached at the endsthereof to in-lead support wires 17a and 17b which are sealed through aglass stem 18 provided with an exhaust and fill tubulation 19. The bult11 may contain mercury and argon or other suitable fill material forsustaining an electric discharge between the electrodes in the lamp.

The electrode 13 is made by the following method. As shown in FIG. 2, aclose wound continuous helical filament 21, preferably made of tungstenwire in a coiled or coiled-coil manner, is attached near the endsthereof to the respective lead wires 17a and 17b, such as by bending theend portions of the wires around the filament in a tight manner so as toclamp and hold the filament. Then, as shown in FIG. 3, an intermediateportion 26 of the filament 21 is temporarily held by means such as asuitable clamp or clip, or by a pronged member 27 having a pair ofprongs 28 and 29 inserted between turns of the filament 21 at places afew turns away from the support wire clamps 22 and 23. Next, as shown inFIG. 4, legs 31 and 32 are pulled on the filament 21, by spreading thesupport wires 17a and 17b relatively apart as indicated by the arrows 33and 34, or by otherwise moving the temporarily held intermediate portion26 of the filament with respect to the support wires 17a and 17b, suchas up or down or sideways, preferably followed by spreading the supportwires 17 relatively apart to make the pulled legs 31 and 32approximately axially straight with respect to the rest of the filament21. Preferably one, two, or three turns of the filament are pulled toform each leg, and each leg preferably is about 3 millimeters long.

The temporary holding means 27 is then removed, and a suitable electronemission mixture or material 36 (FIG. is coated onto the intermediateportion 26 of the filament, which remains in helically wound form. Thelegs 31 and 32 of the filament prevent the emission material 36 fromcreeping or spreading toward the support wire clamps 22 and 23. Currentis then passed through the filament 21, by means of the support wires17a and 17b, to heat the filament to a temperature sufficient tovolatilize and drive off binders or solvents contained in the emissionmaterial 36, and this can be done either before or after sealing theelectrode into a lamp. After removing the temporary holding means, andprior to applying the emission material to the filament, it is desirableto spread the support wires slightly farther apart, to make the filamenttaut and to slightly spread apart the individual turns of the filament,to prevent electrical shorting between adjacent filament turns. Theinvention provides a simple and economical manufacturing method formaking an electrode structure provided with a filament having all theadvantages of the leg mounted type of filament, plus all the advantagesof having the filament in a tightly wound helical form when beinghandled by automated equipment prior to being clamped by the lead wires17a and 17b, thereby preventing tangling and jamming of the filaments inthe automatic handling machinery.

While preferred embodiments of the invention have been shown anddescribed, various other embodiments and modifications thereof willbecome apparent to persons skilled in the art and will fall within thescope of the invention as defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A method of making an electrode comprising the steps of providing ahelically wound filament, attaching said filament near the respectiveends thereof to a pair of support wires, temporarily holding anintermediate portion of said filament, and moving said support wires andsaid intermediate portion of the filament with respect to each other topull out one or more filament turns between the intermediate portion andthe support wires thereby forming legs on said filament between saidintermediate portion and said support wires.

2. A method as claimed in claim 1 in which said step of pulling out oneor more filament turns comprises spreading said support wires apart.

3. A method as claimed in claim 1 in which said step of temporarilyholding an intermediate portion of the filament comprises interposing apair of prongs between turns of the filament at the ends of saidintermediate portion.

4. A method as claimed in claim 1 in which said helically wound filamenthas closely spaced turns along the entire length thereof prior to saidstep of attaching the filament to a pair of support wires.

1. A method of making an electrode comprising the steps of providing ahelically wound filament, attaching said filament near the respectiveends thereof to a pair of support wires, temporarily holding anintermediate portion of said filament, and moving said support wires andsaid intermediate portion of the filament with respect to each other topull out one or more filament turns between the intermediate portion andthe support wires thereby forming legs on said filament between saidintermediate portion and said support wires.
 2. A method as claimed inclaim 1 in which said step of pulling out one or more filament turnscomprises spreading said support wires apart.
 3. A method as claimed inclaim 1 in which said step of temporarily holding an intermediateportion of the filament comprises interposing a pair of prongs betweenturns of the filament at the ends of said intermediate portion.
 4. Amethod as claimed in claim 1 in which said helically wound filament hasclosely spaced turns along the entire length thereof prior to said stepof attaching the filament to a pair of support wires.